What a partial fill means
A partial fill happens when an order you place is executed only for some of the size you requested, rather than in full. In forex this means you might ask to buy or sell a certain number of currency units (or lots) and only a portion of that order is matched immediately at the quoted price. The remaining portion stays open until it can be filled, is cancelled, or is filled later at a different price. Partial execution is simply part of how orders interact with available liquidity in the market.
Trading carries risk. This article explains the mechanics of partial fills in general terms and is not personalised trading advice.
Why partial fills occur in forex
The forex market is large but also fragmented. Liquidity comes from many banks, electronic liquidity providers, and other participants, and the amount available at any single quoted price can change within fractions of a second. Partial fills commonly occur for a few practical reasons.
If you place a large order and there isn’t enough volume available at the price you requested, brokers or liquidity providers will match what they can and leave the remainder. Sudden price movement during execution can also cause only part of the order to transact at the displayed price before the price moves away. In addition, some brokers impose internal size limits per counterparty or per provider; when those limits are reached they will fill only a portion and route the rest elsewhere or leave it pending.
Market fragmentation and variable liquidity are the technical roots; human factors such as trading during news events or outside main sessions (when liquidity is thinner) make partial fills more likely.
How this looks in practice — simple examples
Imagine you want to buy 1,000,000 units of EUR/USD (10 standard lots) at market. The broker connects to several liquidity providers. One provider can offer 600,000 units at 1.12000 but the next best available size at that moment is only 200,000 units at 1.12010 and then 200,000 units at 1.12020. Your order will be filled in parts: 600k at 1.12000, 200k at 1.12010 and 200k at 1.12020. Your trade ticket may show these as separate fills; your effective entry is the volume-weighted average price of the fills.
A limit order gives another example. You place a buy limit for 500,000 units at 1.25000. If only 150,000 units are offered at or below that price before the market moves higher, you’ll receive a partial fill of 150,000. The remaining 350,000 will remain open but may never fill if the price moves away.
These partial fills can happen even with small retail-sized trades during volatile or illiquid conditions, although they are more common with larger sizes.
Order types and how they affect partial fills
Different order types interact with liquidity in different ways. Market orders are intended to execute immediately and will usually be filled — sometimes partially — using prices available across providers until the requested size is exhausted. Limit orders allow you to specify a maximum (for buys) or minimum (for sells) price and therefore are more likely to be partially filled if not enough volume exists at that level.
Some conditional order instructions change how partial fills are handled. “All-or-none” (AON) or “Fill-or-kill” (FOK) request that the order only executes if it can be completed in full; an AON may remain open until a full fill is found, while FOK either fills entirely immediately or is cancelled. “Immediate-or-cancel” (IOC) will fill what it can immediately and cancel any unfilled remainder — in other words an IOC explicitly allows partial fills. Not all brokers or platforms support every instruction, so check your broker’s order options.
How brokers and liquidity providers handle partial fills
Brokers differ in how they route orders and how they report fills. An ECN or STP broker routes orders to external liquidity providers and may show multiple fill lines when an order is matched across several venues. A market-maker or dealing-desk broker may handle some or all of the match internally and could either fill the order fully, partially, or reject the excess depending on their internal liquidity.
Execution reporting also varies: some platforms present each partial execution separately, others report a single averaged fill price. Fees and commissions may apply per executed fill or per order, depending on the broker’s charging structure — multiple partial fills can therefore change the total transaction cost. Because of these differences, reading your broker’s execution policy is important.
Practical strategies to reduce or manage partial fills
You cannot eliminate partial fills completely, but you can reduce their frequency and their impact. One straightforward approach is to avoid placing very large single orders in thinly traded pairs. Splitting a large order into smaller increments and executing over time helps avoid exhausting a single liquidity queue and can reduce slippage.
Timing your trades for periods of higher liquidity — for major session overlaps such as London/New York — usually improves fill quality. Using limit orders with realistic price tolerance can protect against unexpected price moves, but limits also increase the chance of partial fills; combining a limit with an IOC instruction can let you take whatever is immediately available without leaving the rest pending.
If you trade institutional-sized volumes, consider algorithmic execution tools or working with liquidity providers that offer volume-weighted execution algorithms; these tools aim to slice orders and minimise market impact. Finally, test execution behaviour in a demo account and monitor how your broker reports fills so you understand average execution and costs.
Effects on risk management and P&L
Partial fills change your actual entry or exit price and may split your position across different prices. That can complicate stop-loss placement and position-sizing calculations, especially if part of an intended position remains unfilled and you assume the full size is active. If you use a fixed-size stop-loss in pips, a partial fill means the risk per executed unit may differ from the plan; if your remaining size later fills at a worse price your realised average may be less favourable.
For stops and take-profits you should check how your platform handles them when an order is partially filled. Some platforms attach stop and limit orders separately to each fill; others treat position-level stops. Always verify how your broker implements these mechanics to avoid surprises.
Risks and caveats
Partial fills are an execution phenomenon that can materially affect your trades. They can increase transaction costs through additional spreads and commissions, change your effective entry or exit, and interact with margin and risk controls in ways that may be unexpected if you assume immediate full execution. During high-impact news or very thin market conditions, partial fills and wide slippage are more likely.
Brokers have different execution models and terms, and not every broker supports order instructions like AON or FOK. Carefully read your broker’s execution policy and test in a demo environment. This article is educational and not personalised trading advice — consider your own objectives and constraints and, if needed, consult a qualified professional. Remember that trading forex involves risk and you can lose more than your initial deposit if using leverage.
Key takeaways
- Partial fills occur when only part of an order is executed immediately because available liquidity is insufficient at the requested price.
- Large orders, illiquid currency pairs, and volatile conditions increase the chance of partial fills; timing and order type matter.
- You can manage partial fills by splitting orders, trading during liquid sessions, using appropriate order instructions, and testing broker execution.
- Always understand your broker’s execution and fee policies and how partial fills affect stops and position sizing; trading carries risk.
References
- https://fxmerge.com/community/forex-questions/what-is-partial-fill-in-forex/7018
- https://www.forex.com/en-us/glossary/partial-fill/
- https://www.moneyland.ch/en/partial-fill-definition
- https://www.tastyfx.com/help-and-support/orders-stops-and-limits/what-are-partial-fills-and-points-through-current/
- https://www.quantconnect.com/docs/v2/writing-algorithms/reality-modeling/trade-fills/key-concepts
- https://www.babypips.com/forexpedia/fill
- https://www.ig.com/uk/help-and-support/corporate-events-and-dealing-2973c107/trade-orders-and-rejections-a2a27636/spread-betting-and-cfd-order-features-25a2de6c/what-are-partial-fills-and-points-through-current-8c7d9891